The standard approach to store electrical energy is by using electrochemical batteries. Although batteries have undergone several centuries of development, deficiencies remain particularly for applications which recently have become practical or desirable. For example, the general consensus is that a practical, inexpensive electrically driven automobile awaits the development higher capacity, less expensive batteries which can be charged sufficiently to provide a practical radius of operation. Current electrically driven vehicles are not close to being competitive, in cost or performance, with internal combustion engine driven cars and trucks. Although electrically driven vehicles have recently enjoyed considerably improved performance, internal combustion engines have also improved, meaning that the relative advantage of combustion engine vehicles remains substantial.
It is known to use a capacitor to store direct current electrical energy, particularly in smaller capacity sizes. A major problem with capacitors as energy storage devices is they discharge immediately, producing a relatively large burst of energy over a very short time. Often, this does meet the requirements of the device to be driven, i.e. often the driven device requires delivery of energy over a prolonged period of time. In other words, the discharge rate of capacitors is often not matched with the energy rate requirement of a device that is desired to be powered.
Another major problem with capacitors is the voltage declines as energy is discharged. This also produces a mismatch of the characteristics of capacitors compared to the requirements of a device to be driven. The amount of energy stored in a capacitor is a function of the square of the voltage, as follows:energy stored=W=½×C×E2 where W is the energy stored in joules, C is the capacitance of the capacitor in Farads and E is the voltage of the capacitor in volts. As the energy stored in a capacitor is used, the voltage declines so that electrical motors, for example, normally cannot be driven by capacitors for a prolonged length of time.
Disclosures of interest may be found in U.S. Pat. Nos. 5,920,469 and 7,323,849 and Printed Patent Application 2008/0021602.